Adler



Feb. 2, 1960 R. ADLER REMOTE CONTROL SYSTEM 5 Sheets-Sheet 2 OriginalFiled April 16, 1956 INVENTOR.

BY p

ROBERT ADLER N QE HIS ATTORNEYv Feb. .2, 1960 ADLER 2,923,918

REMOTE CONTROL SYSTEM Original Filed April 16, 1956 5 Sheets-Sheet 3l64(Re|dys operate) l63 (Amplifier cut-off) 0 Voltage frequency ROBERTADLER INVENTOR.

HIS ATTORNEY.

Feb. 2, 1960 R. ADLER 2,923,918

REMOTE CONTROL SYSTEM Original Filed April 16, 1956 5 Sheets-Sheet 4ROBERT ADLE R INVENTOR.

FIG. 5

HIS TTORNEY.

Feb. 1960 R. ADLER 2,923,918 REMOTE CONTROL SYSTEM I Original FiledApril 16, 1956 5 Sheets-Sheet 5 Fro'rn Input I Circuit l ROBERT ADL 11vTOR.

WQW

HIS ATTORNEY.

REMOTE CONTROL SYSTEM Robert Adler, Northfield, Ill., assignor to ZenithRadio Corporation, a corporation of Delaware Original application April16, 1956, Serial No. 578,333, now Patent No. 2,821,954, dated February4, 1958. Divided and this application October 30, 1957, Serial No.693,313

3 Claims. (Cl. 340171) This invention is directed to a new and improvedremote control system for controlling operation of an electricalcircuit. The system is particularly valuable when applied to control ofone or more electrical circuits in a wave-signal receiver such as atelevision receiver, and is described in that connection; it is not,however, restricted to this particular use, but may be employed incontrolling apparatus in a wide variety of applications. The presentapplication is a division of the co-pending application of Robert Adler,Serial No. 578,333, filed April 16, 1956, for Control System, now U.S.Patent No. 2,821,954, issued February 4, 1958, and assigned to the sameassignee as the present application.

There are many different types of electrical or electri cally-controlledapparatus for which convenience and efiiciency of operation may begreatly enhanced by a remote control system. For example, a televisionreceiver is best utilized when the observer is seated at a substantialdistance from the receiver, thus making it relatively inconvenient tochange the station or signal channel to which the receiver is tuned whena change in programs is desired, to change the amplitude of sound fromthe receiver, ,to turn the receiver on and off, etc. Accord-1 ingly, itis highly desirable to provide a system to regulate the receiveroperation without requiring the observer to leave the normal viewingposition. Similarly, .it is frequently desirable to provide for remotecontrol of doors, as on a garage, or" heating apparatus, such as afurnace, andof other similar electrical or electrically-controlleddevices. In many of these applications, it is undesirable to have adirect cable connection from the remote control station to thecontrolled device, since awire or cable link is not particularlyattractive in appearance and may often cause accidents when extendedtransversely of an area where people must walk.

Remote control systems in which operating characteristics of a radio ortelevision receiver or other device are varied in response to radio,acoustic, or light signals have been employed in the past. Those systemswhich utilize a portable miniature radio transmitter have generally beenunsatisfactory in that the control system may be triggered to change theoperating characteristics of the controlled device by signals emanatingfrom sources other than the control transmitter. Radio-linked remotecontrol systems frequently create objectionable interference in otherwave signal receivers; they also tend to be relatively complex andexpensive to manufacture and require batteries or some other source ofelectrical power at the transmitter.

Light impulse actuated systems are generally effective in operation, butfrequently are relatively expensive, particularly where a number or"different electrical circuits are to be controlled, since thephoto-sensitive devices employed at the receiving station of the systemare relatively costly. Systems of this type are also sometimes subjectto false actuation under adverse ambient lighting conditions.

Acoustic control systems, using signals in both 'the United StatesPatent M operating characteristics for the .circuit of Figure 2;

2,923,918 Patented Feb. 2, 1960 audible and ultra-sonic ranges, havebeen proposed many times but have not found general acceptance. Thislack of acceptance is generally attributable to the fact that theamplitude of the signal received atthe pick-up station of the systemvaries substantially as the distance between the transmitting andpick-up stations is changed. This factor tends to make a control systembased upon amplitude modulation of an acoustic carrier quite erratic inoperation. In addition, systems of this type are quite frequentlysubject to false triggeringfrom extraneous acoustic signals. When it isdesired to remotely control a plurality of functions of an apparatus,the aforementioned ditficulties are not only proportionally multipliedbut additional difliculties arise from the need to discriminate onecontrol signal from another while yet providing a system in which amaximum number of the components thereof are common to the performanceof all the different control functions in order to achieve the greatesteconomy of cost and space.

It is aprincipal object of this invention, therefore, to provide a newand improved plural-function remotelyactuated control system for anelectrical or electricallycontrolled device which overcomes theabove-noted disadvantages of prior art arrangements.

It is a corollary object of the invention to provide a new and improvedplural-function remote control system for a wave-signal receiver orsimilar device which may be easily incorporated in that device withoutsubstantially modifying its basic construction.

It is a further object of the invention to provide a new and improvedplural-function remote control system of simple and inexpensiveconstruction, wherein a large proportion of the various components maybe common to all the different control functions.

Accordingly, the invention is directed to a remote control system forselectively initiating either one of a pair of different controlfunctions of an apparatus. The system includes a control signal receivercoupled to the apparatus and responsive to either one of a pair ofairborne ultrasonic compressional-wave signals each of a differentfrequency for developing one of a corresponding pair of individualelectrical signals; means coupled to the receiver means are responsiveto the individual electrical signals for initiating the respectivecontrolfunctions of the apparatus. A frequency-discriminatingrectifier-detector is included within the receiver means and has asignal response characteristic including a pair of distinct frequencypeaks individually harmonically related to the respective differentfrequencies. Finally, a remotely located transmitter comprises a pair ofelongated longitudinal-mode vibrators each having a different physicallength respectively equal to one-half wavelength in the vibrator at adifferent one of the frequencies; the transmitter includes manuallyoperable means for selectively exciting the vibrators intolongitudinal-mode vibration.

The features of the invention which are believed to be new are set forthwith particularity in the appended claims. The invention, together withfurther objects and advantages thereof, may best be understood, however,by reference to the following description taken in conjunction with theaccompanying drawings, in which:

Figure l is a block diagram of a remote control system constructed inaccordance with the invention and also shows, in very simplified form, atelevision receiver controlled by the invention;

Figure 2 is a detailed schematic diagram of the receiver circuitry for apreferred embodiment of a remote control system constructed inaccordance with the invention;

Figure 3 is an explanatory diagram showing certainfrequency-discriminator Figure 4 is an explanatory diagram illustratingoperation of integrating circuits in the embodiment of Figure 2;

Figure 5 is a perspective view of a transmitter unit for a remotecontrol system constructed in accordance with the invention; and

Figure 6 is aschematicdiagram of a portion of anotherembodiment of theinvention.

In Figure 1, a conventional television receiver 10 is shown insimplified block diagram form as an example of the type of electricaland/or electrically-controlled apparatus which may be regulated byremote control systems constructed in accordance with the invention.Receiver 10.includes an antenna 11 coupled to a receiving circuit unit12; receiving circuits 12 may include the usual radio-frequencyamplifier, station selector, first detector and intermediate-frequencyamplifier stages found in most conventional receivers. Receivingcircuits 12 are coupled to a second detector 13 which, in turn, iscoupled to a video-amplifier 14, to a sweep system 15, and to the usualaudio circuits 16. The output of video amplifier 14- is coupled'to theelectron gun of a cathoderay image reproducer 17. The output of sweepsystem 15 is coupled to the deflection yoke of the picture tube, hereillustrated schematically by coils 18 and 19. Audio circuits 16 arecoupled through a relay 37 to the usual loudspeaker 20. The operatingcircuits of the receiver are provided with the necessary operatingpotentials from a receiver power supply 21 which is energized from anordinary 115 volt 60 cycle source as indicated by the power input plug22. A tuner motor 23 is mechanically connected to the station-selectionsection of receiving circuits 12 to permit remote .control of this stageof the receiver, as explained in greater detail hereinafter.

The construction and operation of television receiver 113 is entirelyconventional and may be varied as desired without having any effect uponthe invention; accordingly, only an extremely brief description of itsoperation is included here. A television signal is intercepted atantenna 11 and suitably amplified and detected in receiving circuits 12to develop an intermediate-frequency signal which is supplied to asecond detector 13. The second detector develops a composite videosignal which is supplied to video amplifier 14, sweep system 15, Y

and audio circuit 16. The video information portions of the signal areutilized to control the intensity of an electron beam developed inpicture tube 17, whereas the synchronizing signals are employed tocontrol deflection of the beam across the image screen of the picturetube under the influence of the sweep signals developed in systern 15and applied to deflection yoke 18, 19. The audio portion of thecomposite video signal is suitably detected in circuit 16 and employedto energize loudspeaker It will be recognized by those skilled in theart that many changes may be made in the construction of rev ceiver 1t}without departing from conventional practice.

For example, the information signal input for audio circuit 16 may bederived from the output stage of video amplifier 14 rather than fromsecond detector 13; the same change may be made in the signal inputcircuit for sweep system 15. Then too, an electrostatic deflectionsystem may be employed for image reproducer 17 None of these or the manyother possible changes, however, have any substantial effect upon thestructure and operation of the remote control system schematicallyillustrated in Figure 1.

The remote control system of Figure 1 comprises a transmitter 30 whichdevelops four ultrasonic acoustic signals of predetermined minimumamplitude and duration within four distinct restricted non-overlappingfrequency ranges. The structure and operation of a preferred transmitterdevice are described hereinafter in detail in connection with Figure 5.Transmitter 30 constitutes the remote or portable portion of the controlsysterm; the remainder of the apparatus illustrated in Figure 1 ispreferably located closely adjacent to receiver 10 and may beconstructed as an integral part of the receiver. The stationary orreceiving section of the control system comprises an input circuit 31including a microphone 32 coupled to a suitable amplifier 33 of anydesired number of stages. nected to a limiter circuit 34, the outputstage of the limiter being coupled to a pair of series-connectedsegregation networks 35 and 36. Segregation network 35 is connected totwo relays 37 and 38; network 36 is similarly coupled to a pair ofrelays 39 and 40.

Relay 37 includes a switch 47 which is connected in series with one ofthe input leads for loudspeaker 20. Relay 38 comprises a switch 48connected in series with one of the power leads between power-connectionplug 22 and receiver power supply 21. Relays 39 and 40 include switches49 and 50 respectively which are incorporated in the energizing circuitsof tuner motor 23. The remote control system also includes a powersupply 51 having an input circuit connected across the leads-from powerinput plug 22;.control power supply 51 is suitably connected to each ofcircuits 32--36 and to relays As indicated above, the control system isactuated by ultrasonic signals radiated from transmitter 30; forexample, in a given instance transmitter 31} may develop circuitcomprising microphone 32 and amplifier 33 generates an electrical inputsignal having a frequency representative of the received acousticsignal. In the preferred embodiment to be described in greater detailhereinafter in conjunction with Figure 2, the frequency of the inputsignal generated in input circuit 31 is equal to that of the receivedultrasonic signal; however, in some applications it may be desirable toemploy a heterodyning device in the input circuit, in which case thefrequency of the electrical input signal is determined by but notnecessarily equal to that of the received acoustic signal.

The electrical input signal developed in circuit 31 is applied tolimiter 34, which generates an amplitudelimited signal having afrequency equal to an integral multiple of the aforementioned electricalinput signal frequency. In this connection, it should be noted that theterm integral multiple, as used throughout this specification and in theappended claims, refers to multiplication by an integer, includingunity. Preferably, the amplitude-limited signal appearing at the outputof limiter 34 represents a low odd harmonic of the electrical inputsignal such as the third or fifth harmonic. The amplitudelimited signaldeveloped in limiter 34 is applied to segregation networks 35 and 36,which distinguish the desired amplitude-limited signal from extraneoussignals, both within and without the frequency band of the actuatingsignal, which may appear in the output from limiter 34. In theembodiment of Figure 1, four individual circuits in receiver 10 areregulated by the remote control sys Amplifier 33 is in turn con-.

vfiss es a riw rk .1 d- 6ers cons ruc ed askvelop control signalsonly inresponseto signals of predetermined minimum duration and duty cyclewithinrestricted frequency bands respectively including the selectedoperating frequencies. The received signals are distinguished from eachother in networks 35and 36 strictly on a frequency basis.

In order to avoid triggering ofthe control system from extraneousacoustic, electrical, or magnetic signals or stray fields, it is alsonecessary that segregation circuits 35 and 36 be able to analyze thereceived signal on the basis of duration and dutyvcycle. For-thisreason, the two devices each include an integrating system for averagingthe signal received from limiter 31 over an extended period of timesomewhat shorter than the time constant of transmitter 30. Theintegrated signal is then applied to a threshold device which remainsinoperative except during intervals whentheintegrated signal exceeds apreselected minimum value. Consequently, a received signal within thesame frequency range as the acoustic actuating signal but ofsubstantially shorter duration does not result in generation of acontrol signal in the output stages of networks 35 and 36. By the sametoken, an intermittent signal within the acoustic frequency range of thesystem cannot trigger it into operation in most instances, dependingupon the minimum operating level selected for the threshold devicesinthe segregation circuits. Of course, the receiver system can be falselytriggered by a received signal of relative constant amplitude within theacoustic frequency range of the system; however, this is not likely tooccur in most locations.

When the received signal is in the proper frequency range and meets thesystem requirements with respect to duration and duty cycle, relay 37,for example, may be actuated. A ratchet or step-type relay is employedfor relay 37 so that the audio system of receiver 10 may be alternatelyenergized and muted by successive actuations of the relay. Accordingly,when the sound output from speaker exceeds the level of comfort or whensilence is momentarily desired, transmitter may be actuated to emit thenecessary ultrasonic signal to operate relay 37 and open the audio inputcircuit to speaker 20; upon the next actuation of relay 37, audiooperation is restored. A similar step-type or ratchet relay is employedas relay '38, which serves to energize or de-energize receiver 10completely. Of course, the signal from transmitter 30 employed toactuate relay 39 is at a different frequency from that utilized inoperating relay 37, the two different actuating signals beingdistinguishedfrom each other on a frequency basis by circuits and 36.

Operation of the tuner control relays 39 and 40 is essentially similarto that of relays 37 and 38 except that the motor-control relays arepreferably of the instantaneous-contact type. In the illustrated system,a reversible motor is employed; switch 49 of relay 39 is connected inthe motor-energizing circuit employed for clockwise rotation, whereasswitch 50 of relay 40 is connected in the energizing circuit utilizedfor counter-clockwise rotation. An acoustic signal having a frequencydiiferent from those used for control of relays'37 and 38 is employed toactuate relay 39, and an acoustic signal of a fourth distinctivefrequency actuates relay 40. The motor-control circuits areessentially'similar to those long used in the art in connection withother types of remote control systems and consequently are not describedin detail in this specification.

Figure 2 is a detailed schematic diagram of a preferred embodiment ofthe invention comprising a microphone 62 of the variable-capacitancetype; one terminal of the microphone is grounded and the other iscoupled to the control electrode 64 of a first amplifier tube such as apentode 63 by means of an RC coupling circuit comprising-a seriescapacitor 65 and;further comprising a shunt 1resistorl-t66 connectedbetwcen-,.electrode 6.4 and ground.

The m o h t italwi c u es t e sc ewe nected resistors 67, 68 and 69which connect microphone 62 back to the positive or 3+ term nal of thecontrol power supply 51. Cathode 70 of amplifier tube 63 is connected toground through a bias resistor 71 which is bypassed by a capacitor 72."The suppressor electrode 73 of the tube is connected directly to thecathode, and the screen electrode -7,4 is connected to the B+ supplythrough a resistor 75, the screen being by-passed to ground through acapacitor 76.

The output circuit for tube 63 comprises a parallelresonant circuitincluding an inductance 77 and a cacapacitor 78; the tuned circuit isconnected in series between the anode 79 of tube v63 and the 13+ supply.Anode 79 is also coupled to the control electrode 80 of the pentodesection 81A of a combined pentode-triode by means of an RC couplingcircuit comprising a series coupling capacitor 82 and a self-biasingresistor 83 which connects control electrode 80 to ground. Tube section81A forms a part of the second stage of the input amplifier of thesystem and includes a cathode 84 which is connected directly to ground,the suppressor electrode 85' in this amplifier stage being connecteddirectly to the cathode. The screen electrode 86 is coupled to aconventional biasing circuit comprising a resistor 87 which connects thescreen electrode to the B+ supply and a capacitor 88 bypassing thescreen electrode to ground.

The output circuit for amplifier section 81A is a conventional RCcoupling cir uit which couples the anode 90 of tube section 81A to thecontrol electrode 91 of a triode tube section 81B. The coupling circuitincludes a load resistor 92 connecting anode 90 to 13+, a capacitor 93and a resistor 94 connected in series between anode 90 and controlelectrode 91, and a coupling resistor 95 connecting the terminal ofcapacitor 93 opposite anode 90 to ground. Triode section 818 comprisesthe third and final stage of the input amplifier of the system, andincludes a cathode 96 which is connected to ground and an anode 97connected t 13+ through a load resistor 98. Accordingly, the circuit asthus far described corresponds directly to the input circuit 31 ofFigure 1.

In the embodiment of Figure '2, input circuit 31 is coupled to a limitercircuit 34 by a coupling capacitor 100 connected in series between anode97 of tube section 81B and the control electrode 101 of a limiter tube102; the input circuit for tube 102 also includes a tuned circuitcomprising an inductance 103 and a capacitor 104 connected in parallelwith each other between control electrode 101 and ground. In theillustrated embodiment, tube 102 is of the gated-beam type commerciallyavailable under the type designation 6BN6. Limiter tube 102 includes acathode 105 connected to ground through an unbypassed biasing resistor106. "The limiter tube fur ther includes a pair of acceleratingelectrodes 107 and 108 disposed on opposite .sides of control electrode101; the two accelerating electrodes are connected to each other and areconnected .to the B+ supply through a resistor 109, being bypassed toground by a capacitor 1 10. Tube 102 further includes a second controlelectrode 111 and an anode or output electrode 11; 2;the second controlelectrode is not utilized in operation of the limiter and may beconnected to anode- 112 as shown or to ground.

Anode 112 of limiter tube 102 ,is returned to B+ through a circuitcomprising two anti-resonant circuits 115 and 116 connected in serieswith each other. The terminal of resonant circuit 115 connected to anode112 is coupled to the electrical center of an inductance 117 through acoupling capacitor 118, and-a capacitor 119 is connected in parallelwith coil 11,7.to form .an antiresonant circuit tuned to the .san efrequency as circuit 115. Coil 117 is also inductively coupled to theinductance coil of tuned circuit 115. The opposite terminals of coils117 are respectively connected to the two anodes 120 and 121 of adoublediode 122. The cathode 123 of tube 122 amociatedwith anode 121 is 7connected back to the electrical midpoint of coil 117 through a resistor124, and the cathode 126 associated with anode 120 is returned to thesame point through a resistor 1'27. Cathodes 123 and 126 are bypassed toground by capacitors 129 and 130 respectively and are returned to asource of negative operating potential C in control power supply 51through two equal resistors 131 and 132 respectively. Tube 122 is thusincorporated in a conventional balanced frequency-discriminator circuitfrequently used as a detector for frequency-modulated signals. In thepresent invention, however, the balanced frequency discriminator is usedin a somewhat different manner than in conventional practice, as will bemade more apparent in the operational description of the system includedhereinafter.

The frequency-discrimination device comprising tube 122 forms a part ofthe first segregation network 35 (see Figure 1); network 35 alsoincludes further means for distinguishing between desired and undesiredoutput signals from limiter 34 on the basis of duration and duty cycleof the received signal. A pair of resistors 133 and 134 are connected inseries with each other and with cathode 123 of tube 122, and a similarpair of resistors 135 and 136 are connected in series with each otherand with cathode 126. The common terminal of resistors 133 and 134 isbypassed to the common terminal of resistors 135 and 136 by a capacitor137; the other terminal of resistor 134 is bypassed to ground through acapacitor 138, whereas the corresponding terminal of resistor 136 isbypassed to ground through a capacitor 139. Resistors 133- 136 andcapacitors 137-139, together with resistors 131 and 132, constitute apair of integrating networks for developing potentials indicative of theaverage amplitudes of the signals appearing at the cathodes of thefrequency-discriminator rectifying-detector comprising tube 122.

Network 35 further includes a threshold device or amplifier comprising adouble triode 140. The two cathodes 141 and 142 of tube 140 aregrounded; the control electrode 143 associated with cathode 141 isconnected to the common terminal of resistor 134 and capacitor 138,whereas the control electrode 144 associated with cathode 142 issimilarly connected to the common terminal of resistor 136 and capacitor139. The anode 145 of tube 140 associated with cathode 141 and controlelectrode 143 is returned to B+ through the operating coil 147 of themuting relay 37 (see Figure 1). Similarly, the other anode 148 of tube140 is connected to the B+ supply through the operating coil 149 of theon-oif relay 38 (Figure 1).

Tuned circuit 116 is incorporated in the second segregation network 36which, as indicated in the description of Figure 1, is similar inconstruction to network 35. Network 36 comprises a second tuned circuit150 coupled to a double diode 151 and to resonant circuit 116 in thesame manner as in discriminator 35; the two cathodes of tube 151 areconnected to a dual integrating network 152 which in turn controlsoperation of a threshold amplifier comprising a double triode 153. Oneof the anodes 154 of amplifier tube 153 is connected to the 13+ supply,through the operating coil 155 of the clockwisemotor-control relay 39,whereas the other output electrode 156 of tube 153 is returned to B+through the operating coil 158 of the counter-clockwise-motor-controlrelay 40.

The basic operation of the control system receiver 7 station illustratedin Figure 2 is similar to that described in connection with Figure 1;Figure 2, however, illustrates several featuers of the invention whichprovide for greatly enhanced effectiveness in plural-function-controlsystem operation as compared with other possible embodiments. Anacoustic signal impinging upon microphone 62 effectively varies themicrophone capacitance and excites the three-stage amplifier comprisingtubes 63, 81A, and 81B. The electrical signal variations provided by themicrophone are first amplified in tube 63, the tuned output circuit 77,78 of the tube providing for substantial attenuation of most frequencycomponents outside of the selected acoustic frequency range of thesystem (38 to 41 kilocycles in the assumed example). The electricalsignal from amplifier tube 63 is further amplified in tubes 81A and 81Band constitutes the input signal applied to limiter tube 102. Furtherfrequency selection is provided by the parallel-resonant circuit 103,104 in the input circuit of the limiter.

Limiter 34, comprising tube 102, performs two distinct functions. Itoperates as a limiting amplifier, providing an output signal of constantamplitude over a wide range of input signal amplitudes. The tubeselected for this limiter must have an output electrode current vs.control electrode voltage characteristic comprising two controlelectrode voltage ranges of substantially zero transconductanceseparated by a control electrode voltage range of high transconductance,a characteristic best achieved by a gated-beam tube such as the 6BN6 butalso attainable in other conventional devices such as the 6BE6 or 6BU8.With a tube and circuit exhibiting this characteristic, the limiterfunctions also as a harmonic generator and provides substantial outputsignals at the third and fifth harmonics of the input signal. Thestructure and operation of a harmonic generator of this type aredescribed in detail in US. Patent No. 2,681,994 to Robert Adler, filedSeptember 27, 1949, issued June 22, 1954, and assigned to the sameassignee as the present invention. Accordingly, a detailed descriptionof operation of the limiter circuit is unnecessary here. It issufficient to indicate that the limiter develops an amplitudelimitedsignal having a frequency which is an integral multiple of the inputsignal frequency; in the illustrated embodiment, the third harmonic ofthe input signal fre quency is utilized for reasons indicatedhereinafter. Any other type of limiter may of course be substituted forthe illustrated device, particularly where the discriminators of thesystem are constructed to operate at the fundamental frequency of theoutput signal from limiter 34. Moreover, it should be understood thatone stage of the amplifier of circuit 31 may be constructed as afrequency multiplier, in which case circuit 34 may function only as alimiter.

The amplitude-limited signal from limiter 34 is supplied to the tunedcircuits and 116 of the discriminators included in networks 35 and 36respectively. The two discriminator input circuits are preferablyconnected in series as illustrated; this is possible because they aretuned to substantially different frequencies and each represents arelatively low impedance at the resonant frequency of the other. In theillustrated system, as in Figure 1, four acoustic signals of differentfrequency are utilized for four different control functions; thefrequencies selected, may, for example, be 38, 39, 40, and 41 kc.respectively. With these operating frequencies, parallel-resonantcircuit 115 may be tuned to a frequency of 38.5 kc., the centerfrequency between the two lowerfrequency signals, in which case resonantcircuit 116 is tuned to 40.5 kc., the median for the twohigher-frequency signals. Operation in this case is predicated upon useof the fundamental component of the output signal from limiter 34.Operation on the fundamental, however, presents difiicult problems infeedback between the circuit elements, particularly the inductances, ofdiscriminator devices 35 and 36 and the different stages of the inputamplifier circuit, particularly the tuned circuit 77, 78 incorporated inthe output circuit of amplifier tube 63. The possibility of suchregeneration difliculty 1S apparent from the fact that the relativelylow frequencies involved make magnetic shielding difficult and expensiveand the further fact that amplification in the system must be extremelyhigh in order to provide for use of relatively weak acoustic triggeringsignals. Consequently, 1n the preferred system illustrated resonant cir-"across resistor 131 is plotted in Figure 3 as "the frequency of thesignal applied to the awith respect to the C- reference*cuitIISistunedto 115.5 kc,, the third'harmonic of the median frequencyfor the two lower-frequency signals. Similarly, circuit '116 isconstructed to have a resonant :frequency of 121.5 kc., the thirdharmonic of the median for the two higher-frequency trigger signals.

In accordance with the usual construction of frequency discriminators,the resonant circuit comprising-coil 11 7 and capacitor 119 is tuned tothe same frequency (115.5 kc.) as resonant circuit 115 and the coils ofthe two circuits are disposed in mutual coupling relationship.

Consequently, the discriminator rectifying-detector comprisingthe twotuned circuits, tube 122, coupling capaci- 101' 118 and resistors 124and 127 has an operating characteristic as illustrated by dash line 160in Figure 3, in which the voltage appearing across cathodes 123 and 126is plotted as a function of the frequency of the signal applied to tunedcircuit 115 from limiter 34. Curve 166 is representative of themagnitude of that voltage; however, it should be understood that thepolarity is arbi- 'trarily selected. As drawn, the curverepresents thepotential of cathode 123 with respect tocathode 126; if cathode 123 had,instead, been chosen as potential reference, curve 160 would appearreversed. It will be'noted that curve 160 is a plot of frequency vs.potential-outputlevel; curve 160 includes two frequency-displaced peaks,illustrated as occurring at 114 and 117 kilocycles, individuallyrepresenting potentials of opposite polarity with respect to thepotential represented by the curve at a frequency, 115.5 kilocycles inthis instance, intermediate the frequencies represented by the peaks.Resistors 131 'and'132, of substantially equal resistance are connectedin series across the two cathodes 123 and 126, their com- :mon terminalbeing returned to the C- reference voltage. Half the discriminatoroutput voltage, therefore, appears across each of these resistors. Thevoltage a'function of discriminator, its amplitude'is apdiscriminatoroutput positive and negative voltage to which the common terminal ofresistors 131 and 132 is returned.

The voltage across resistor 132 illustrated by dotted line '162,'followsa characteristic essentially similar to that of curve 161 except thatthe polarity with respect to the bias voltage is reversed.

The circuit parameters for the discriminator circuits are so selectedthat the two peaks of each of voltage characteristic curves 160162 arecentered at 114 and 117 kcs. respectively, these frequencies being thethird harmonics of the two acoustic frequencies (38 and 39 kcs.)employed to actuate this portion of the control system. In conventionaluse of the discriminator circuit as a detector for frequency-modulatedsignals, only the relatively linear portion of characteristic 160centered about the median or resonant frequency of 115.5 kcs. would beemployed. In thetpresent instance, however, .theeffective operatingrange for the frequency discriminator is restricted to two narrowportions,.each including one of the two peaks at 114 and 117 kcs. toenable being illustrated by solid line 161; proximately half that of thetotal voltage and includes values both LthC system to distinguish.between these two frequencies :andto discriminate against otherfrequencies outside the two operating ranges. For this reason, the twothreshold amplifier sections coupled to cathodes 123 and 126 are'biasedto be'normally cut off except when the input signal from thediscriminator exceeds a predetermined amplitude. The cut-01f level forthe amplifier is indicated by dash line 163 in Figure 3. A somewhathigher amoperate relays 3740 (Figures 1 and 2), since a minimum .currentis required to actuate the relays. The

pl1tude,1nd1cated in Figure 3 by line 164,1s required to resistors-131and 132 to the negative source C -;of trol power supply 51.

Under well-controlled environmental conditions, .it-is only necessary todistinguish between the components of the amplitude-limited signal fromlimiter 34 on the basis of frequency, in which case the thresholdamplifier or amplitude-discriminator device comprising double triode maybe connected directly to resistors 131 and 132 without providing theintervening integrating network shown in the preferred embodiment. Thecontrol sys tem may then be triggered, however, by extraneous ultrasonicsignals having a frequency approximately equal to the selected acousticoperating frequencies or by noise at approximately 114 kc. or 117 kc. inthe output from limiter 34. In a more normal environment, the systemmight thus be triggered into spurious operation by acoustic signals ofvery short duration produced by the jingling of coins or keys or fromother sources. The system might also be falsely actuated by intermittentsignals within the operating acoustic frequency ranges. In order toavoid this possibility of malfunction of the system and take advantageof the slow decay of the ultrasonic signal produced by the transmitter,the integrating network is utilized to average the output signal fromthe frequency discriminator comprising tube 122 over a predeterminedperiod of time, preferably somewhat shorter than the time constant ofthe acoustic transmitter. By properly selecting the circuit parametersfor the integrating network and the threshold or firing levels for thetwo sections of amplifier tube 140, segregation network 35 may be maderesponsive only to signals of predetermined minimum duration and dutycycle.

The effect of the integrating circuit is illustrated in Figure 4, inwhich solid-line curve 165 represents the output voltage of thefrequency discriminator as a function of time for an amplitude-limitedsignal at 114 kc. corresponding to a received actuating signal of 38 kc.from the system transmitter. Dash-line curve 166, on the other hand,indicates a typical noise signal which might occur over a similar timeinterval; the noise signal may vary substantially in frequency and/oramplitude during that period and, as a consequence, the output voltagefrom the frequency discriminator fluctuates considerably. The firinglevel for the threshold amplifier comprising tube 140 is indicated bydash-line 164; as indicated by the shaded areas 167 and 168, the noisesignal would actuate the amplifier section comprising electrodes 141,143 and (Figure 2), even in the absence of a desired actuating signalfrom the transmitter, if no integrating network were interposed betweentube 140 and the output resistors 131 and 132 of the frequencydiscriminator.

The integrated signal impressed upon control electrode 143 of tube 140in response to input signal is illustrated by dash-line 169. Asindicated, control electrode 143 is driven to a potential substantiallyabove cut-off level 164 for a period of time substantially equal to theperiod of conduction which would be provided by signal 165 if nointegrating network were present, althrough the period of conduction forthe amplifier is somewhat delayed. The periods of spurious actuationindicated by shaded areas 167 and 168, however, are completelyeliminated by the integrating circuit, as shown by curve 170, whichrepresents the integrated voltage applied to control electrode 143 as aresult of the noiseinduced output voltage 166 from the frequencydiscriminator. It is thus apparent that the integration circuit ofsegregation network 35 renders the system responsive only to signals ofpredetermined minimum duration as indicated by the time period 171 inFigure 4.

At the same time, the output signal from the frequency discriminationportion of circuit 35 must have a minimum duty cycle in order to triggerthe system. For a .circuit having the characteristics illustratedinFigure 4,

the minimum duty cycle for rapidly fluctuating signals from thediscriminator is determined by the relative amplitudes of maximumlimiter output level 165 and relay actuation level 164 and is equal toapproximately 65%. That is, a fluctuating signal of maximum amplitudemust be present 65% of the time during a period at least equal to thetime constant of the integrating circuit, generally indicated at 172. Ithas been found that a minimum duty cycle of 50%, determined byestablishing relay actuation level 164 at at least 50% of limiter 165,should be maintained to provide adequate noise immunity.

It is thus apparent that the first section of tube 140 comprisingcathode 141, control electrode 143 and anode 145 is rendered conductiveonly when the amplitudelimited signal applied to circuit 115 fromlimiter 34 is sufficiently close to the frequency corresponding to theselected acoustic operating frequency (38 kc.) and has a predeterminedminimum duration and duty cycle. Consequently, a control potential orcurrent is applied to operating coil 147 of relay 37 only when theseconditions obtain, so that muting relay 37 is actuated between itsdifferent operating conditions only in response to the desired acousticsignal from transmitter 30 (Figure 1). Similarly, the other section ofamplifier tube 140 comprising electrodes 142, 144, and 148 (Figure 2) isrendered conductive only in response to a received acoustic signalmeeting the same requirements as to duration and duty cycle and having afrequency very nearly equal to 39 kc., so that coil 149 of on-otl relay38 is actuated only at the desired times. Segregation network 36functions in exactly the same manner to actuate the two motorcontrolrelays 39 and 40 only in response to signals of predetermined durationand duty cycle having frequencies approximately equal to 40 and 41 kc.respectively. In this connection, it should again be noted that the twosegregation circuits 35 and 36 may be identical in construction exceptthat the resonant frequency for circuits 116 and 150 is made equal to121.5 kc. instead of 115.5

One problem presented in the circuit illustrated in Figure 2 is that ofimbalance between the output signals developed by the two frequencydiscriminator circuits, which is generally attributable to theplate-to-ground capacitance of limiter tube 102. This lack of balancebetween the two frequency discriminators can be substantial and canpresent a severe problem in the control system receiver. It has beendiscovered, as described and claimed in the copending application ofRobert Adler and John G. Spracklen, Serial No. 632,124, filed January 2,1957, for Frequency Discriminating System, now U.S. Patent No.2,838,668, issued June 10, 1958, and assigned to the same assignee asthe present application, that the discriminators of networks 35 and 36can be constructed to effectively neutralize this capacitive effect bysuitable positioning of the inductance coils of the frequencydiscriminator tuned circuits. In essence, this is accomplished bylocating the coils of resonant circuits 115 and 116 relatively close toeach other and with connections of proper polarity .so that the mutualinductance linking the two frequency discriminators effectivelycompensates for the plate capacitance of the limiter tube. In onesatisfactory construction employed for this purpose, the four coils ofthe discriminator circuits areall aligned in a single row, the twoinside coils constituting the inductances of circuits 115 and 116. Withthis arrangement, the coil spacing may be adjusted to provide thenecessary controlled coupling and, if there is insufiicient spaceavailable in the control receiver chassis to avoid overcoupling, excessmutual coupling can be compensated by adding a relatively smallcapacitor between limiter tube anode 112 and ground.

Of course, the remote control system is only as good as its transmitter,and it has been found that complexity and delicacy of construction arehighly undesirable in mitter 200 for use in the remote control system ofthe invention is illustrated in Figure 5, in which complete details aregiven for only one section 205 of 'the transmitting apparatus inasmuchas the four sections required to actuate the systems illustrated inFigures 1 and 2 may be essentially identical except for their resonantfrequencies.

Acoustic transmitter section 205 comprises a vibrator element or rod 201of homogeneous material having an overall length L equal to one-halfWavelength of sound in that material at a predetermined acousticoperating frequency. Stated differently, the resonant frequency forvibrator rod 201 is approximately equal to the velocity of sound in therod material divided by twice the length L. The diameter D of vibratorrod 201 is preferably made approximately equal to one wavelength at theresonant frequency in air, to provide for good efiiciency in radiatingthe acoustic signal. Rod 201 is supported by a spring clamp 202 affixedto a bracket 203; spring clamp 202 should be located at the midpoint ofthe rod to permit longitudinal-mode vibration of the rod. This supportincluding spring clamp 202 is described and claimed in the copendingapplication of Ole Wold, Serial No. 645,310, filed March 11, 1957, forUltrasonic Generator, now U.S. Patent No. 2,821,956, issued February 5,1958, and assigned to the present assignee. Bracket 203 is suitablyaffixed to a support base 204.

this portion of the system. A preferred form of trans- Vibrator element201 constitutes the resonant transmitting element for the firsttransmitter section 205; the complete transmitter 200 includes threeother essentially similar transmitter sections which differ from section205 only in the length of their individual vibrator elements. Provisionis thus made for the four different acoustic operating frequenciesnecessary for actuating the control systems illustrated in Figures 1 and2.

Transmitter section 205 further includes a pushbutton 206 affixed to anoperating rod 207 which is slidably supported in a pair of spacedbrackets 208 and 209. A bias spring 210 is mounted on operating rod 207to urge the pushbutton operating rod toward its normal or inactiveposition. A cam lever 211 is pivotally mounted on one side of operatingrod 207 by means of a pin 212 and is biased for rotation in acounterclockwise direction by a spring 213 connected between a fixedpoint on operating rod 207 and an extension 214 of the cam lever. A stopelement 215 mounted on lever 211 engages op erating rod 207 to maintainthe cam lever in its normal inoperative position as illustrated. Anextension 216 of cam lever 211 engages a slot 217 in a trip rod 218which is slidably mounted in brackets 208 and 209 for movement parallelto operating rod 207; trip rod 218 is biased toward its normalinoperative position, as illustrated, by a spring 219. One end of rod218 extends beyond bracket 209 and is employed to support a strikingelement in the form of a hammer 220, hammer 220 being mounted on aresilient support bracket 221 affixed to the trip rod. A damping element225 is afiixed to rod 207 and extends into contact with vibrator element201 at the end of the vibrator element adjacent hammer 220; the dampingelement may, for example, comprise a length of resilient steel wire.Certain details of this striking mechanism are described and claimed inthe copending application of Robert C. Ehlers and Clarence W. Wandrey,Serial No. 645,091, filed March 11, 1957, for Ultrasonic Transmitter,now U.S. Patent No. 2,821,955, issued February 4, 1958, and assigned tothe present assignee.

To actuate transmitter section 205, pushbutton 206 is depressed in thedirection indicated by arrow A. As

the operating shaft 207 moves in this direction, cam lever 211 moveswith it and the cam lever extension 216, by its engagement in slot 217,forces trip rod 218 in the same direction. When operating rod 207 hasmoved through a predetermined distance, an extension 222 on cam lever211 engages a stop element 223 atnxed to bracket 209.

Consequently, continued movement of operating M3207 inthe directionindicated by arrow A causes the cam lever to rotate in a clockwisedirection and releases cam extension 216 from slot 217 in trip rod 218.The trip rod moves rapidly in the direction indicated by arrow T,thereby impinging hammer 2220 upon the end of vibrator rod 201 andexciting the vibrator rod into longitudinal mode vibration.

Amplitude of vibration in rod decays exponentially in essentially thesame manner as an electrical sig 'nal in a shock-excited resonantcircuit. The time constant for the resonator rod is dependent upon therate at which the vibratory energy stored in the rod is radiated intothe air and upon the internal damping of the rod. These two factors, inturn, are functions of the material from which the vibrator rod isconstructed. An extremely wide variety of materials may be employed forthis purpose, including metals, glass, ceramics, and others. In order toachieve a signal of useful amplitude over a period of substantialduration, it is desirable to select a material which exhibits relativelylow internal damping at'the desired operating frequency. A typicalexample of such material is aluminum, for which the time constant at afrequency of 40 kc. is of the order of 0.3 second and which exhibits a Qof the order of 35,000. The length of the vibrator rod, if made ofaluminum, is relatively small at the suggested operating frequencies inthe 40 kc. range, being only approxin'iately 2.5 inches.

The amplitude of the signal from transmitter section 205, as it impingesupon the microphone 62 (Figure 2) is inversely proportional to thedistance separating the transmltter from the receiver portion of thecontrol system. Obstructions in the direct line of sight, standing wavepatterns caused by reflections and other factors may contributeadditional attenuation. Consequently, a transmitter designed to providean acoustic signal of sufficient amplitude to actuate the reciverreliably from a distance of 30 feet, for example, may continue todevelop an output signal of sufiicient strength to actuate the controlsystem over a much longer time interval than desired when operated at adistance of only 10 feet from the receiver. In the case of the ratchetor step-type relays empioyed for the on-off and muting functions of thesystem, this effective extension of duration of the acoustic signal mayhave little or no adverse effect. With respect to theinstantaneous-contact tuning control relays, however, it may easilycause the receiver to overshoot the desired tuning condition, thusseriously impairing the effectiveness of the control system.Consequently, it is desirable to include some means for damping thevibrator element of the transmitter under control of the transmitteroperator. This damping effect is readily achieved by moms of dampingelement 225. When pushbutton 206 is depressed to actuate transmittersection 205, the damper element is removed from contact with vibratorrod 291 and consequently does not interfere with vibration of theresonant rod. 'As-soon as pushbutton 206 is released, however, andreturns to its normal position, damping element 225 again contactsvibrator rod 201 and effectively damps the vibrator so that it cannotcontinue to radiate an acoustic signal. overshooting in the tuningcontrols is thus effectively avoided.

The longitudinal-mode vibratory system of the transmitter of Figure 5provides marked advantages as compared to other types of acoustic signalgenerators. For example, prismatic bars subjected to vibration in thefundamental flexure mode could be employed. For a device of this type,however, it is necessary to utilize a vibrator constructed from materialmuch heavier than aluminum since the rate of energy loss to thesurrounding air is much higher for a fiexure mode. Thus there would beno saving in weight, even though the flexure-mode device could be madesubstantially smaller in size. Highcarbon steel could perhaps providesatisfactory performance, but it would introduce a substantialdisadvantage 14 due to "the factthat the resonant irequeney of a steelbarwould be a function of the drawing temperature employedin fabricatingthe bar. In addition, the frequency of a prismatic fiexure bar islinearly proportional to the thickness of the bar and lI'lVBISiZif/proportional to the square of its length. Consequently, to obtain afrequency tolerance of one part in one thousand, a bar of approximatelyone inch length and one-half inch thickness would have to be machined toapproximately 1.00025 inch tolerances in both length and thickness. Alongitudinalrnode vibrator such as rod 201, on the other hand, has avresonant frequency which depends only on its length, being inverselyproportional thereto. Consequently, the resonant frequency of a 2.5 inchrod machined to $0025 inch, a ten times wider tolerance than the onementioned above, is accurate to within one part in one thousand. itwould be much too expensive to maintain the tolerances indicated for heflexure mode resonator, so that individual adjustment of the frequencyof each resonator would be necessary; this is not usually necessary withlongitudinal-mode vibrators. Considerations similar to those just givenin connection with prismatic bars apply to other shapes such as bells,chimes and the like which utilize flexure modes.

Figure 6 illustrates the segregation network sections of anotherembodiment of the invention which is otherwise similar to thatillustrated in Figure 2. In the embodiment of Figure 6, anode 112 oftube 182 in limiter 34 is connected to the 8+ supply through fourseries-connected coils 250, 251, 252, and 253. Coil 250 forms theprimary winding'of a transformer 254 having a secondary winding 255which, with a capacitor 256, forms a parallel-resonant circuit tuned toa frequency of 114 kcs. One terminal of coil 255 is connected to theanode 257 of a diode 258, the cathode 259 of the diode being returned tothe other terminal of coil 255 through a D.C. load resistor 260 which isshunted by a capacitor 261. The bottom terminal of 'coil 255 is alsoreturned to the negative DC. voltage supply C. Cathode 259 of diode 258is also connected to the control electrode 262 of an amplitudediscriminator or threshold amplifier tube 263 through an integratingcircuit comprising two resistors 264 and 265, connected in seriesbetween cathode 259 and control electrode 262,

and apair of shunt capacitors 266 and 267. The cathode 268 of tube 263is grounded and the anode 269 is connected to muting relay coil 147 (seeFigure 2). Tunedsecondary transformer 254, diode 258, tube 263, andtheir associated circuitry comprise a'frequency and amplitudesegregation network indicated by dash outline 270.

Coil 251 constitutes the primary winding of a tunedsecondary transformer271 which is coupled to a threshold amplifier comprising a tube 272,by'means of a diode 273 and anintegrating circuit, thereby forming asegregation network 274 which is essentially similar to circuit 270. Theembodiment of Figure 6 also includes a third similar amplitude andfrequency segregation circuit 276 including coil 252 as the primarywinding of a tunedsecondary transformer 277, a diode 278, and a suitableintegrating circuit coupling diode 278 to a threshold amplifier tube279. A fourth segregation network 280 is included in the apparatus ofFigure 6; discriminator 280 is essentially similar to devices 270, 274,and 276. Network 280 includes a tuned-secondary transformer 281, a diode282, and an integrating circuit connecting diode 282 to the controlelectrode of a threshold amplifier tube 283.

In many respects, operation of segregation circuits 270, 274. 276 and280 is essentially similar to that of circuits 35 and 36 of Figure 2.The secondary windings of transformers 254, 271, 277, and 281 are tunedto 114, 117, 120, and 123 kc. respectively to provide for selectionbetween the four different third-harmonic signals supplied from limiter34. In each instance, the signal is rectified by the diode in thesegregation circuit, integrated, and applied to the threshold amplifiertube.

Y 15 Tubes 263, 272, 279 and 283 are each normally biased beyond cut-01fby means of the connection of their control electrodes to negative biassource C- and are rendered conductive only when a signal within alimited frequency range is applied to the tuned transformer secondaryrectified, integrated, and supplied to the control electrode. Like theembodiment of Figure 2, therefore, the apparatus of Figure 5 applies acontrol signal to the individual relay coils only when the receiver istriggered by an acoustic signal within a limited frequency range andhaving a predetermined minimum duration and duty cycle. The circuit ofFigure 6 is somewhat less noiseimmune than that of Figure 2, since anysignal within the overall operating range of the segregation circuits270, 274, 276, and 280 tends to produce a control signal of the correctpolarity to render the threshold amplifier tubes conductive, whereas inthe frequency discriminator circuits of Figure 2 noise having arelatively uniform frequency distribution produces no control potentialat the threshold or amplitude-discrimination tubes, thereby aifordingadditional protection against spurious operation. In addition, becausethe frequency discriminator devices of Figure 2 each utilize two tunedcircuits, they are, generally speaking, somewhat more frequencyselective.

Of course, other types of acoustic transmitter apparatus can be employedin conjunction with the receiver control systems of Figures 1, 2 and 6and the transmitter of Figure 5 may be employed in other acousticsystems,

, but the two portions of the control system in combination complementeach other to form a highly efiicient and relatively inexpensive controlsystem. The number of transmitter sections 205 required is of coursedependent upon the number of control functions provided for in thereceiver system. In this connection, it should be noted that additionalsegregation devices such as networks 35 and 36 (Figures 1 and 2) orcircuits 270, 274, 276 and 280 (Figure 6) may be added to the controlsystem to permit regulation of other electrical circuits and, similarly,additional transmitter sections corresponding to section 205 (Figure 5)may be added to the transmitter unit to actuate the additionalsegregation devices. By the same token, if it is desired to controlfewer electrical circuits, the remote control system may becorrespondingly simplified as by eliminating segregation network 36(Figures 1 and 2) or devices 276 and 280 (Figure 6) in a system in whichonly two electrical circuits are to be controlled. A correspondingreduction in transmitter sections is of course made possible in thesimpler control system. The control system is thus extremely flexiblewith respect to the number of electrical circuits it may be utilized toactuate.

The control system of the invention permits accurate and effectiveregulation of any number of electrical circuits without requiringsubstantial modification of the device in which those circuits areincorporated. The system is essentially immune to false actuation undernormal operating circumstances and is quite simple and inexpensive inconstruction both at the transmitter and ree ceiver terminals of thesystem. While particular embodiments of the present invention have beenshown and described, it is apparent that changes and modifications maybe made without departing from the invention in its broader aspects. Theaim of the appended claims, therefore, is to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

I claim:

1. in a remote control system for selectively initiating either one of apair of different control functions of an apparatus, the combinationcomprising: control signal receiver means coupled to said apparatus andresponsive to either one of a pair of airborne ultrasoniccompressional-wave signals each of a different predetermined frequencyfor developing one of a corresponding pair of individual electricalsignals; a frequency-discriminating rectifier-detector included withinsaid receiver means and having a signal response characteristicincluding a pair of distinct frequency peaks individually harmonicallyrelated to the said respective different frequencies; first and secondswitch means independently responsive to difierent signals individuallyat respective ones of said pair of frequency peaks for initiatingrespective diiferent ones of said control functions; a remotely locatedtransmitter comprising a pair of elongated longitudinal-mode vibratorseach having a different physical length respectively equal to' one-halfwavelength in the vibrator at a different one of said predeterminedfrequencies; and manuallyoperable means included in said transmitter forselectively exciting said vibrators into longitudinal-mode vibration.

2. A remote control system as defined in claim 1 in which said signalresponse characteristic constitutes a frequency vs.potential-output-level curve comprising two frequency-displaced peaksindividually representing potentials of opposite polarity with respectto the potential represented by said curve at a frequency intermediatethe frequencies represented by said peaks.

3. A remote control system as defined in claim 1 in which saidlongitudinal-mode vibrators each have a diameter approximately equal toone wavelength in air at said different frequencies.

References Cited in the file of this patent UNITED STATES PATENTSAndrews et al Mar. 20, 1956

